Among the agricultural inputs to augment food production, use of fertilizer, in particular urea plays a key role. It is estimated that the present global consumption of fertilizer N is in the order of 77 Tg annually which is estimated to be increased to 144 Tg by the beginning of next century. In India, the present consumption of fertilizer N is about 9.5 m tons which is estimated to be increased to 14 m tons by 2001. Utilization efficiency of fertilizer N seldom exceeds 50%; it is yet low in paddy.
When applied to soil, urea hydrolyses by enzyme urease to from NH.sub.4 and finally to NO.sub.3 by some bacteria. The NH.sub.4 is subjected to loss by volatilization whereas NO.sub.3 is prone to losses through leaching and dentrification. Apart from increasing the cost of cultivation in agriculture, N losses through leaching as well as in gaseous form have direct concern in environmental degradation. As a consequence of leaching NO.sub.3 concentration in ground water has been increasing at an alarming rate. Any strategy that can restrict or retard these processes, would reduce the loss of N. The present invention deals with finding strategies for retarding urea transformation and nitrification for a higher fertilizer N use efficiency.
Researchers have tried to reduce the losses of N (i) by applying N in small doses at different growth stages of crop, so that the plants use it before it is lost and (ii) by deep placement or incorporating the urea in soil. The ammonium produced can be retained for sometimes in the exchange complex of soil clay particles.
Some of the modern tools suggested are (I) use of urease inhibitors such as phenylphosphorodieamidate (PPD), hydroxamates and benzoqauinones (Gould, W D et al 1986, Adv. Agron. 40: 209-238), which reduce the hydrolysis of urea and this can reduce ammonia volatilization lossess, and (ii) use of nitrification inhibitors such as N serve or nitrapyrin (2-chloro-6(tricholoromethyl)-pyridine), DCD (dicyandiamide), AM (2-amino 4-chloro-6-methylpyrimidine), KN.sub.3 (potassium azide) and thiourea (Sahrawat, 1989, Adv.Agron 42: 279-302, Prasad and Power, 1995, Adv. Agron 54: 233-81).
These compounds have been successful in some parts of the world. However, because of cost and poor availability these could not be made commercially popular to common farmer. An interesting discovery was the nitrification inhibitory properties of neem seed cake (Prasad et al, 1971, Adv. Agron 23: 337-381) and neem cake coated urea and has found some favour among Indian farmers. Neem bittern/extracts such as Nimin, Neemex etc. for treating urea are in Indian market. More recently a neem oil urea emulsion adduct has also been reported (Prasad et al. 1998. Curr. Sci. 75: 15). Many of the fertilizer mixture, coated materials specially synthetic chemicals are put to limited use such as in turf or in high price agriculture such as commercial floriculture and that to in developed countries and have not reached the general farmers due to high costs.